A well-known, time-honored method of incorporating creatorship information into a work of art is the application of a signature to the work itself. In the case of a two-dimensional image, such as a photograph, the signature typically obliterates the information it overlies, and is therefore applied to a peripheral portion of the image. Although the signature has the desirable attribute of ready availability to anyone possessing the image, it may interfere with proper use of the image or be otherwise distracting or annoying to the viewer. This problem also persists in the realm of digitally represented data, in which it would be desirable, for example, to mark photographs or other types of images as proprietary material before electronic publication or distribution through on-line services, or to vary the signatures marking different versions in order to identify different routes of distribution.
Data hiding is a class of processes used to embed recoverable (e.g., signature) data in digitally represented information, such as a host image, with minimal degradation to the host information. Although the changes introduced by embedded data may be perceptible by a human observer, they need not be conspicuous. The goal of data hiding is not to restrict access to the host information, but rather to add the signature information to the host so that they can be distributed together. The ability to embed inconspicuous data makes data hiding attractive for adding signature information to digital and analog images.
Several known low-bit data hiding techniques afford encoding of information in a minimally perceptible fashion. Typically, however, recovery of the embedded data requires recreating specific details of the embedding process. Although this restriction makes the encoded information highly resistant to unauthorized removal, this resistance is generally purchased at the price of excluding the typical consumer of the image from accessing the encoded ownership or copyright information.